Optical radiation detector

ABSTRACT

The system comprises two propagators and receivers for the detection of submarine wakes. The propagators irradiate oil films in submarine wakes thereby causing the oil to fluoresce. The fluorescent emanations from adjacent areas of the oil and detected by the receivers which provide an appropriate indication.

1111 3,745,566 14 1 July 10, 1973 OPTICAL RADIATION DETECTOR 2,972,9242/1951 Clemens 356/4 3,043,903 1 1962 M d [75] Inventor schenecady' NY3,078,453 211963 14420 512111 et a]. 343/5 [73] Assignee: The UnitedStates of America as lthe secret? of the Primary Examiner-Carl D.Quarforth Navy washmgton Assistant Examiner-J. M. Potenza [22] Filed:June 14, 1962 Attorney-Raymond l. Tompkins, Louis B. Applebaum 1] pp No202 635 and Philip Schneider 52 US. Cl. 343/5 R, 250/833 uv, 340/4 RABSTRACT 51. 1111.01 001s 9/00 Th 7 r. r .7 d W 58 Field of Search250/71, 71.5, 83.3 UV, 6 Pmpagaw for the detection of submarine wakes.The propagators 250/833 71 G; 343/5 5 irradiate oil films in submarinewakes thereby causing the oil to fluoresce. The fluorescent emanationsfrom [56] References Cited adjacent areas of the oil and detected by thereceivers which provide an appropriate indication. UNITED STATES PATENTS2,587,976 3/1952 DeMent 250/71 18 Claims, 1 Drawing Figure w/vc/fl/vcf 56/1074 away 7 14 0/6470? Mae/vs MZfl/VS (DPTICAL RADIATION DETECTOR Thisinvention relates to detection apparatus and especially to a system forthe detection of submarine wakes by means of radiation.

It has been found that an oil film appears in the wake of a submarine,presumably as a consequence of the destruction of tiny marine animallife. This oil film can be made to fluoresce by exposure to ultravioletradiation.

The objects and advantages of the present invention are accomplished byirradiating oil films in submarine wakes with radiation such asultraviolet light which causes the oil to fluoresce. Fluorescentemanations from adjacent areas of the oil are received by a pair ofreceivers sensitive to such radiation, the receivers being focused onadjacent areas of the oil film. The output of these receivers is fed toan indicating instrument through a coincidence circuit so that the meterprovides an indication only when both receivers are receivingfluorescent emanations.

An object of the invention is to detect fluorescent radiation.

Another object is to detect oil residues.

A further object is to detect submarines by means of the oil films leftin submarine wakes by marine organisms.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

The FIGURE is a schematic representation of an embodiment of theinvention.

The components of the invention comprise a pair of ultraviolet-radiationpropagators 11 and 11' and a pair of fluorescent-radiation receivers 13and 13', coincidence circuit means 24 and means for indicating an outputsignal 26. The propagators and receivers are preferably located alongthe wings of an airplane and the rest of the radiation detector islocated inside the airplane.

The propagators and receivers comprise two identical sets, each setconsisting of one propagator and one receiver. Examining the first set,propagator 11 and receiver 13, it can be seen that the ultravioletradiation propagator 111 comprises a large parabolic mirror 12, a sourceof ultraviolet radiation 14 located at the focal point of the mirror 12,and a filter 16 which transmits ultraviolet light and absorbs otherfrequencies of light. If the airplane is to be used at a height of about1,000 feet, a parabolic mirror with a diameter of three feet irradiatesa spot 29 on the ocean surface 28 slightly over three feet in diameter.The ultraviolet source 14 may, for example, be a high-pressure mercury(8H4) lamp. The ultraviolet-transmission filter 16 can be made of Coming9863 glass, for example.

The fluorescent-radiation receiver 13 comprises a filter 18 forabsorbing ultraviolet light, a parabolic mirror 22 and a photomultipliertube located at the focal point of the mirror 22.

The propagator 11 and the receiver 13 are both oriented to focus on thesame spot 29 on the ocean surface 28. Since reflected and scatteredradiation from the propagator should be excluded from the receiver, anultraviolet-absorption filter 18 is employed and the plane containingthe propagated and received beams of radiation is not perpendicular tothe surface of the ocean.

The coincidence circuit means 24 comprises any suitable coincidencecircuit and an amplifying circuit. The signal indicator means 26 may beany suitable meter, for example.

The photomultiplier outputs are fed into the coincidence circuit means24 which provides an output only when the output of bothphotomultipliers is above a predetermined level (an increase in detectedfluorescent radiation above the normal level). The coincidence circuitminimizes noise due to thermal radiation or reflected night radiationfrom the ocean surface.

Although it is not apparent in the FIGURE because of limitations ofspace, the spot 29' upon which the beam of the second propagator 11' isfocused is adjacent to the spot 29 upon which the beam of the firstpropagator 11 is focused. This minimizes the possibility ofnon-detection of a submarine wake because the air plane is travelingparallel to the wake.

Although the system has been described as a system for the detection offluorescent radiation, it can also be used to detect small changes inthe reflectivity of oilcovered water. Reflectivity changes during thedaytime can be detected by employing ultraviolet light of shortwavelength (2,800 angstrom units) and suitable filters at the receivers.The short-wavelength ultraviolet light has the advantage that it isstrongly absorbed by almost all organic materials so that the presenceof an oil film leads to a significant change in reflectivity. However,if the system is used in this manner, the plane containing thepropagated and reflected waves should be perpendicular to the surface ofthe ocean and the filters at the receivers should be filters whichtransmit ultraviolet light rather than filters which absorb it.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:

1. A radiation detector comprising, in combination:

a pair of radiation propagators, each oriented to irradiate a differentspot on a surface;

a pair of radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals are applied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

2. A radiation detector comprising, in combination:

a pair of focusable radiation propagators, each oriented to irradiate adifferent spot on a surface;

a pair of focusable radiation receivers, each oriented to receiveradiation from a different one of said irradiated spots, and eachproviding an electrical output signal when radiation is received,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

3. A radiation detector comprising, in combination: a pair of focusableradiation propagators, each oriented to irradiate a different spot on asurface;

a pair of focusable radiation receivers, each oriented to receiveradiation from a different one of said irradiated spots, and eachproviding an electrical output signal when radiation is received,

said irradiated spots being adjacent to each other on said surface, 7

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

4. A radiation detector comprising, in combination:

a pair of radiation propagators, each oriented to irradiate a differentspot on a surface;

a pair of radiation receivers which are sensitive to a differentspectral band of radiation than that projected by said propagators, eachreceiver oriented to receive radiation from a different one of saidirradiated spots, and each providing an electrical output signal whenradiation is received,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

5. A radiation detector comprising, in combination: a pair of focusableradiation propagators, each oriented to irradiate a different spot on asurface;

a pair of focusable radiation receivers which are sensitive to adifferent spectral band of radiation than that projected by saidpropagators, each receiver oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

6. A radiation detector comprising, in combination: a pair of focusableradiation propagators, each oriented to irradiate a different spot on asurface;

a pair of focusable radiation receivers which are sensitive to adifferent spectral band of radiation than that projected by saidpropagators, each receiver oriented to receive radiation from adifferent one of said irradiated spots, andeach providing an elec- Wtrical output signal when radiation is received, said irradiated spotsbeing adjacent to each other on said surface,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

7. A radiation detector comprising, in combination: a pair ofultraviolet-radiation propagators, each oriented to irradiate adifferent spot on a surface;

a pair of fluorescent-radiation receivers, each oriented to receiveradiation from a different one of said irradiated spots, and eachproviding an electrical output signal when radiation is received,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

8. A radiation detector comprising, in combination:

a pair of focusable ultraviolet radiation propagators,

each oriented to irradiate a different spot on a surface;

a pair of focusable fluorescent radiation receivers, each oriented toreceive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

9. A radiation detector comprising, in combination:

a pair of focusable ultraviolet radiation propagators,

each oriented to irradiate a different spot on a surface;

a pair of focusable fluorescent radiation receivers, each oriented toreceive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,

said irradiated spots being adjacent to each other on said surface,

said propagators and receivers being spaced from said surface, and

the plane containing the propagated and received beams beingnon-perpendicular to said irradiated surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, and output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

10. A radiation detector for the detection of submarine wakescomprising, in combination:

a pair of radiation propagators, each oriented to irradiate a differentspot on a surface,

each said propagator comprising a focusing mirror, a source ofultraviolet radiation located at the focal point of said mirror, and anultraviolettransmission filter located in the path of the beam projectedby said mirror;

a pair of radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said propagators and receivers being spaced from said surface, and theplane containing the propagated and received beams beingnon-perpendicular to said irradiated surface,

each said radiation receiver comprising a focusing mirror,radiation-sensitive means located at the focal point of said mirrorproducing an electrical signal in response to irradiation, and aradiation filter located in the path of the radiation beam received bysaid mirror, said radiation filter passing a different spectral band of.radiation than that emanating from said radiation propagators;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

11. A radiation detector for the detection of submarine wakescomprising, in combination:

transmission filter located in the path of the beam projected by saidmirror;

a pair of radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said propagators and receivers being spaced from said surface, and theplane containing the propagated and received beams beingnon-perpendicular to said irradiated surface,

each said radiation receiver comprising a focusing mirror, radiationsensitive means located at the focal point of said mirror producing anelectrical signal in response to irradiation, and a radiation filterlocated in the path of the radiation beam received by said mirror, saidradiation filter passing a different spectral band of radiation thanthat emanating from said radiation propagators; V

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

12. A radiation detector for the detection of subma rine wakescomprising, in combination:

a pair of radiation propagators, each oriented to irradiate a differentspot on a surface,

each said propagator comprising a focusing mirror, 21 source ofultraviolet radiation located at the focal point of said mirror, and anultraviolettransmission filter located in the path of the beam projectedby said mirror;

a pair of radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said propagators and receivers being spaced from said surface, and theplane containing the propagated and received beams beingnon-perpendicular to said irradiated surface,

each said radiation receiver comprising a focusing mirror,photomultiplier means located at the focal point of said mirrorproducing an electrical signal in response to irradiation, and aradiation filter located in the path of the radiation beam received bysaid mirror, said radiation filer passing a different spectral band ofradiation than that emanating from said radiation propagators;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

13. A radiation detector comprising in combination:

a pair of radiation propagators, each oriented to irra diate a differentspot on a surface;

a pair of radiation receivers which are sensitive to a differentspectral band of radiation than that projected by said propagators, eachreceiver oriented to receive radiation from a different one of saidirradiated spots, and each providing an electrical output signal whenradiation is received,

said propagators and receivers being spaced from said surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircit means.

14. A radiation detector comprising, in combination: a pair of focusableradiation propagators, each oriented to irradiate a different spot on asurface;

a pair of focusable radiation receivers which are sensitive to adifferent spectral band of radiation than that projected by saidpropagators, each receiver oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said propagators and receivers being spaced from said surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

15. A radiation detector comprising, in combination: a pair of focusableradiation propagators, each oriented to irradiate a different spot on asurface;

a pair of focusable radiation receivers which are sensitive to adifferent spectral band of radiation than that projected by saidpropagators, each receiver oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received,

said irradiated spots being adjacent to each other on said surface,

said propagators and receivers being spaced said surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

116. A radiation detector comprising, in combination: a pair ofultraviolet-radiation propagators, each oriented to irradiate adifferent spot on a surface;

a pair of fluorescent-radiation receivers, each orifrom ented to receiveradiation from a different one of said irradiated spots, and eachproviding an electrical output signal when radiation is received,

said propagators and receivers being spaced from said surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

17. A radiation detector comprising, in combination:

a pair of focusable ultraviolet radiation propagators, each oriented toirradiate a different spot on a sur face;

a pair of focusable fluorescent radiation receivers, each oriented toreceive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,

said propagators and receivers being spaced from said surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

18. A radiation detector comprising, in combination:

a pair of focusable ultraviolet radiation propagators,

each oriented to irradiate a different spot on a surface;

a pair of focusable fluorescent radiation receivers, each oriented toreceive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,

said irradiated spots being adjacent to each other on said surface,

said propagators and receivers being spaced from said surface;

coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and

signal-indicating means connected to the output of said coincidencecircuit means.

1. A radiation detector comprising, in combination: a pair of radiationpropagators, each oriented to irradiate a different spot on a surface; apair of radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received, said propagators and receiversbeing spaced from said surface, and the plane containing the propagatedand received beams being non-perpendicular to said irradiated surface;coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 2. A radiation detectorcomprising, in combination: a pair of focusable radiation propagators,each oriented to irradiate a different spot on a surface; a pair offocusable radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received, said propagators and receiversbeing spaced from said surface, and the plane containing the propagatedand received beams being non-perpendicular to said irradiated surface;coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 3. A radiation detectorcomprising, in combination: a pair of focusable radiation propagators,each oriented to irradiate a different spot on a surface; a pair offocusable radiation receivers, each oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received, said irradiated spots beingadjacent to each other on said surface, said propagators and receiversbeing spaced from said surface, and the plane containing the propagatedand received beams being non-perpendicular to said irradiated surface;coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 4. A radiation detectorcomprising, in combination: a pair of radiation propagators, eachoriented to irradiate a different spot on a surface; a pair of radiationreceivers which are sensitive to a different spectral band of radiationthan that projected by said propagators, each receiver oriented toreceive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,said propagators and receivers being spaced from said surface, and theplane containing the propagated and received beams beingnon-perpendicular to said irradiated surface; coincidence circuit meansto which the output signals from said receivers are applied as inputsignals, an output signal being provided by said coincidence circuitmeans whenever both input signals are applied simultaneously; andsignal-indicating means connected to the output of said coincidencecircuit means.
 5. A radiation detector comprising, in combination: apair of focusable radiation propagators, each oriented to irradiate adifferent spot on a surface; a pair of focusable radiation receiverswhich are sensitive to a different spectral band of radiation than thatprojected by said propagators, each receiver oriented to receiveradiation from a different one of said irradiated spots, and eachproviding an electrical output signal when radiation is received, saidpropagators and receivers being spaced from said surface, and the planecontaining the propagated and received beams being non-perpendicular tosaid irradiated surface; coincidence circuit means to which the outputsignals from said receivers are applied as input signals, an outputsignal being provided by said coincidence circuit means whenever bothinput signals are applied simultaneously; and signal-indicating meansconnected to the output of said coincidence circuit means.
 6. Aradiation detector comprising, in combination: a pair of focusableradiation propagators, each oriented to irradiate a different spot on asurface; a pair of focusable radiation receivers which are sensitive toa different spectral band of radiation than that projected by saidpropagators, each receiver oriented to receive radiation from adifferent one of said irradiated spots, and each providing an electricaloutput signal when radiation is received, said irradiated spots beingadjacent to each other on said surface, said propagators and receiversbeing spaced from said surface, and the plane containing the propagatedand received beams being non-perpendicular to said irradiated surface;coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 7. A radiation detectorcomprising, in combination: a pair of ultraviolet-radiation propagators,each oriented to irradiate a different spot on a surface; a pair offluorescent-radiation receivers, each oriented to receive radiation froma different one of said irradiated spots, and each providing anelectrical output signal when radiation is received, said propagatorsand receivers being spaced from said surface, and the plane containingthe propagated and received beams being non-perpendicular to saidirradiated surface; coincidence circuit means to which the outputsignals from said receivers are applied as input signals, an outputsignal being provided by said coincidence circuit means whenever bothinput signals are applied simultaneously; and signal-indicating meansconnected to the output of said coincidence circuit means.
 8. Aradiation detector comprising, in combination: a pair of focusableultraviolet radiation propagators, each oriented to irradiate adifferent spot on a surface; a pair of focusable fluorescent radiationreceivers, each oriented to receive radiation from a different one ofsaid irradiated spots, and each providing an electrical output signalwhen radiation is received, said propagators and receivers being spacedfrom said surface, and the plane containing the propagated and receivedbeams being non-perpendicular to said irradiated surface; coincidencecircuit means to which the output signals from said receivers areapplied as input signals, an output signal being provided by saidcoincidence circuit means whenever both input signals are appliedsimultaneously; and signal-indicating means connected to the output ofsaid coincidence circuit means.
 9. A radiation detector comprising, incombination: a pair of focusable ultraviolet radiation propagators, eachoriented to irradiate a different spot on a surface; a pair of focusablefluorescent radiation receivers, each oriented to receive radiation froma different one of said irradiated spots, and each providing anelectrical output signal when radiation is received, said irradiatedspots being adjacent to each other on said surface, said propagators andreceivers being spaced from said surface, and the plane containing thepropagated and received beams being non-perpendicular to said irradiatedsurface; coincidence circuit means to which the output signals from saidreceivers are applied as input signals, and output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 10. A radiation detector forthe detection of submarine wakes comprising, in combination: a pair ofradiation propagators, each oriented to irradiate a different spot on asurface, each said propagator comprising a focusing mirror, a source ofultraviolet radiation located at the focal point of said mirror, and anultraviolet-transmission filter located in the path of the beamprojected by said mirror; a pair of radiation receivers, each orientedto receive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,said propagators and receivers being spaced from said surface, and theplane containing the propagated and received beams beingnon-perpendicular to said irradiated surface, each said radiationreceiver comprising a focusing mirror, radiation-sensitive means locatedat the focal point of said mirror producing an electrical signal inresponse to irradiation, and a radiation filter located in the path ofthe radiation beam received by said mirror, said radiation filterpassing a different spectral band of radiation than that emanating fromsaid radiation propagators; coincidence circuit means to which theoutput signals from said receivers are applied as input signals, anoutput signal being provided by said coincidence circuit means wheneverboth input signals are applied simultaneously; and signal-indicatingmeans connected to the output of said coincidence circuit means.
 11. Aradiation detector for the detection of submarine wakes comprising, incombination: a pair of radiation propagators, each oriented to irradiatea different spot on a surface, said spots being adjacent to each other,each said propagator comprising a focusing mirror, a source ofultraviolet radiation located at the focal point of said mirror, and anultraviolet-transmission filter located in the path of the beamprojected by said mirror; a pair of radiation receivers, each orientedto receive radiation from a different one of said irradiated spots, andeach providing an electrical output signal when radiation is received,said propagators and receivers being spaced from said surface, and theplane containing the propagated and received beams beingnon-perpendicular to said irradiated surface, each said radiationreceiver comprising a focusing mirror, radiation sensitive means locatedat the focal point of said mirror producing an electrical signal inresponse to irradiation, and a radiation filter located in the path ofthe radiation beam received by said mirror, said radiation filterpassing a different spectral band of radiation than that emanating fromsaid radiation propagators; coincidence circuit means to which theoutput signals from said receivers are applied as input signals, anoutput signal being provided by said coincidence circuit means wheneverboth input signals are applied simultaneously; and signal-indicatingmeans connected to the output of said coincidence circuit means.
 12. Aradiation detector for the detection of submarine wakes comprising, incombination: a pair of radiation propagators, each oriented to irradiatea different spot on a surface, each said propagator comprising afocusing mirror, a source of ultraviolet radiation located at the focalpoint of said mirror, and an ultraviolet-transmission filter located inthe path of the beam projected by said mirror; a pair of radiationreceivers, each oriented to receive radiation from a different one ofsaid irradiated spots, and each providing an electrical output signalwhen radiation is received, said propagators and receivers being spacedfrom said surface, and the plane containing the propagated and receivedbeams being non-perpendicular to said irradiated surface, each saidradiation receiver comprising a focusing mirror, photomultiplier meanslocated at the focal point of said mirror producing an electrical signalin response to irradiation, and a radiation filter located in the pathof the radiation beam received by said mirror, said radiation filterpassing a different spectral band of radiation than that emanating fromsaid radiation propagators; coincidence circuit means to which theoutput signals from said receivers are applied as input signals, anoutput signal being provided by said coincidence circuit means wheneverboth input signals are applied simultaneously; and signal-indicatingmeans connected to the output of said coincidence circuit means.
 13. Aradiation detector comprising in combination: a pair of radiationpropagators, each oriented to irradiate a different spot on a surface; apair of radiation receivers which are sensitive to a different spectralband of radiation than that projected by said propagators, each receiveroriented to receive radiation from a different one of said irradiatedspots, and each providing an electrical output signal when radiation isreceived, said propagators and receivers being spaced from said surface;coincidence circuit means to which the output signals from saidreceivers are applied as input signals, an output signal being providedby said coincidence circuit means whenever both input signals areapplied simultaneously; and signal-indicating means connected to theoutput of said coincidencE circuit means.
 14. A radiation detectorcomprising, in combination: a pair of focusable radiation propagators,each oriented to irradiate a different spot on a surface; a pair offocusable radiation receivers which are sensitive to a differentspectral band of radiation than that projected by said propagators, eachreceiver oriented to receive radiation from a different one of saidirradiated spots, and each providing an electrical output signal whenradiation is received, said propagators and receivers being spaced fromsaid surface; coincidence circuit means to which the output signals fromsaid receivers are applied as input signals, an output signal beingprovided by said coincidence circuit means whenever both input signalsare applied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 15. A radiation detectorcomprising, in combination: a pair of focusable radiation propagators,each oriented to irradiate a different spot on a surface; a pair offocusable radiation receivers which are sensitive to a differentspectral band of radiation than that projected by said propagators, eachreceiver oriented to receive radiation from a different one of saidirradiated spots, and each providing an electrical output signal whenradiation is received, said irradiated spots being adjacent to eachother on said surface, said propagators and receivers being spaced fromsaid surface; coincidence circuit means to which the output signals fromsaid receivers are applied as input signals, an output signal beingprovided by said coincidence circuit means whenever both input signalsare applied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.
 16. A radiation detectorcomprising, in combination: a pair of ultraviolet-radiation propagators,each oriented to irradiate a different spot on a surface; a pair offluorescent-radiation receivers, each oriented to receive radiation froma different one of said irradiated spots, and each providing anelectrical output signal when radiation is received, said propagatorsand receivers being spaced from said surface; coincidence circuit meansto which the output signals from said receivers are applied as inputsignals, an output signal being provided by said coincidence circuitmeans whenever both input signals are applied simultaneously; andsignal-indicating means connected to the output of said coincidencecircuit means.
 17. A radiation detector comprising, in combination: apair of focusable ultraviolet radiation propagators, each oriented toirradiate a different spot on a surface; a pair of focusable fluorescentradiation receivers, each oriented to receive radiation from a differentone of said irradiated spots, and each providing an electrical outputsignal when radiation is received, said propagators and receivers beingspaced from said surface; coincidence circuit means to which the outputsignals from said receivers are applied as input signals, an outputsignal being provided by said coincidence circuit means whenever bothinput signals are applied simultaneously; and signal-indicating meansconnected to the output of said coincidence circuit means.
 18. Aradiation detector comprising, in combination: a pair of focusableultraviolet radiation propagators, each oriented to irradiate adifferent spot on a surface; a pair of focusable fluorescent radiationreceivers, each oriented to receive radiation from a different one ofsaid irradiated spots, and each providing an electrical output signalwhen radiation is received, said irradiated spots being adjacent to eachother on said surface, said propagators and receivers being spaced fromsaid surface; coincidence circuit means to which the output signals fromsaid receivers are applied as input signals, an output signal beingprovided By said coincidence circuit means whenever both input signalsare applied simultaneously; and signal-indicating means connected to theoutput of said coincidence circuit means.